pull-offs, where, after striking one note, specifically marked notes can be played by fingering the correct buttons but without strumming. There are also note portions of some songs where notes appear semi-transparent relative to normal notes; these notes, introduced in Guitar Hero World Tour, can be played simply by tapping the correct buttons on the controller without strumming or using a touch-sensitive "slider bar" below the fret buttons, if the player is using a World Tour controller. Bass players can play open chords by strumming without holding any fret buttons. Warriors of Rock introduces sustained open chords for bass players, although unlike other sustainable notes, does not require you to hold down the button required to execute the note initially. Drum players, when using velocity-sensitive drum kits, may be presented with both ghosted notes or notes with a shield icon over them; these represents drum notes that should be struck softer or harder than normal, respectively, to score more points. Drum players can also attach a second bass drum pedal, necessary for certain songs in the "Expert+" difficulty. If the player successfully matches a number of consecutive notes correctly, they boost their individual scoring multiplier up to a maximum 4x value; missing a note will reset to the multiplier back to 1x. Throughout each song's respective charts for the instruments are special highlighted phrases; completing all the notes in this phrase, and for guitar/bass players, using the whammy bar on marked sustained notes, fills part of a Star Power meter. When this meter is at least half full, the player can activate Star Power by performing special actions on their controllers: either tilting the guitar controller upward briefly or pressing the Star Power activation button for guitar and bass; striking two pads simultaneously on the drums; and either double tapping the microphone or pressing one of the buttons on the game console's regular controllers for vocals. When Star Power is activated, the overall band scoring multiplier is increased for a limited time until the Star Power meter is drained. After completing a song, the band is awarded a number of stars based on the overall score; in normal modes for Warriors of Rock, up to six stars can be earned; the final being achievable only through zero misses and zero extra strums. A major addition in Warriors of Rock is the use of special powers that come from special "warrior"